Figure 1

Schema of three triplex motifs bind to TTS by different orientation. This schema shows three triplex motifs of third sequence strand which can form triplex structure with polypurine of duplex (or TTS) via Hoogsteen or reverse Hoogsteen hydrogen bond. In CT motif, the third strand is parallel with TTS by forming Hoogsteen hydrogen bond. In the GT motif, the third strand can be either anti-parallel to the third strand by forming reverse Hoogsteen or parallel by forming Hoogsteen hydrogen bond. In GA motif, the third strand is anti-parallel with TTS by forming.